Heating, ventilating, and air-conditioning (HVAC) systems have been used to maintain desirable temperatures and humidity levels within buildings, and buildings have been constructed with ventilation systems, including HVAC systems, to provide comfortable and safe environments for occupants to live and work. To maintain fresh air within buildings and to reduce the level of indoor air contaminants, in many applications, at least a portion of the air handled by ventilation or HVAC systems has been taken from outdoors, while a portion of the indoor air handled by HVAC systems has been exhausted, for example, to outside the building.
In many situations, outside air introduced to the building to replace exhaust air must be cooled or heated before being introduced to the building to provide temperatures within desired parameters, and often must be dehumidified or humidified to keep humidity levels within desired ranges. But adding or removing heat or humidity (moisture) typically involves the expenditure of energy. To reduce the energy required to condition the outside air, recovery wheels and desiccant-based dehumidification wheels, including passive dehumidification wheels, have been used to transfer heat, moisture, or both, between exhaust air and incoming outside air. Examples of the prior art in these areas are described in U.S. Pat. Nos. 4,769,053 and 6,199,388, and U.S. patent application publication number 2004/0000152, all having at least one inventor in common with the subject matter of this document, and all of which are incorporated herein by reference in their entirety. Certain terms, however, may be used differently in the documents that are incorporated by reference, and if any conflicts exist, this document shall govern herein. These prior art documents also describe many of the potential needs and benefits of such systems and the use of recovery wheels.
In addition, cooling coils have been used to cool and dehumidify outdoor air that is introduced to a building, including cooling coils that are cooled with chilled water that has been cooled by one or more chillers. Furthermore, U.S. Pat. No. 6,199,388 describes systems and methods for controlling temperature and humidity that include a recovery wheel, a passive dehumidification wheel, and a cooling coil, wherein the system forms a supply airstream that passes outdoor air first through the recovery wheel, then through the cooling coil, then through the desiccant-based passive dehumidification wheel, and then to the space, and the system forms an exhaust airstream that passes return air from the space first through the desiccant-based passive dehumidification wheel, and then through the recovery wheel. Examples of prior art systems are shown in FIGS. 2 and 4.
Further, chilled beams have been used to cool spaces within buildings. Patent application publication No. 20130199772 describes active and passive chilled beams and is also incorporated herein by reference. Active chilled beams have been used wherein outdoor air is cooled and dehumidified to become supply air, which is delivered to the chilled beams where the supply air is released into the space through slots or nozzles in a manner that causes induction of room air across a cooling coil positioned within the chilled beam, thereby substantially increasing cooling capacity delivered to the space. Lower levels of humidity in the supply air would be beneficial in some such situations because the chilled beams themselves do not remove humidity from the room air and the supply air may be the only source of dehumidification. Further still, in chilled beam applications, humidity levels in the room air can limit the amount of cooling that can be provided through the chilled beams because the chilled beams cannot be cooled below the room air dew point or else condensation will occur on the chilled beams which will drip on the occupants and other contents of the space. Avoiding such condensation is necessary or beneficial in many situations.
Still further, chillers that produce chilled water have been used as an efficient way to provide cooling and dehumidification, particularly for large buildings. In chilled water systems, however, the minimum temperature that the air leaving the cooling coil can reach has been limited by how cold the chilled water can be produced using traditional chiller performance limitations. As a result, the amount of humidity that can be removed from the outdoor air, for example, is limited. Lower levels of humidity in the supply air, however, would be beneficial in some situations, for example, where chilled beams are used. In addition, supply air volume (i.e., flow rate) is often desired to be greater than exhaust air volume to achieve proper building pressurization to prevent infiltration, but in prior art systems, particularly when the imbalance between supply air volume and exhaust air volume is sufficiently high, condensation has occurred within the exhaust airstream, for instance, on the dehumidification wheel or between the dehumidification wheel and the recovery wheel. Avoiding such condensation would be beneficial, if not essential, in many situations. Moreover, in prior art systems, when supply air was cooled in the cooling coil sufficiently to provide the desired level of supply air humidity, supply air temperatures were often colder than desired. Warmer supply air temperatures would be beneficial in such situations. Needs and opportunities for improvement exist for partially or fully providing one or more of these needs or potential benefits. Room for improvement exists over the prior art in these and various other areas that may be apparent to a person of ordinary skill in the art having studied this document.